A direct current circuit breaker (DC circuit breaker) is used to interrupt a fault current when a fault occurs on a direct current transmission line used as a high voltage transmission line. A direct current transmission line for a high voltage is used as a transmission line for a high voltage of 50 kV or higher of a high voltage direct current (HVDC) transmission system or a transmission line for a medium voltage of 50 kV or lower of a medium voltage direct current (MVDC) distribution system.
A DC circuit breaker is provided with a relatively inexpensive mechanical switch to interrupt a fault current when a fault occurs on a DC transmission line. The mechanical switch is opened to interrupt a fault current, thereby preventing a faulty system from influencing a normal system when a fault occurs in a high voltage direct current (HVDC) transmission system or a medium voltage direct current (MVDC) distribution system.
However, when the mechanical switch is opened to interrupt a fault current, an arc is generated in the mechanical switch due to a high voltage applied thereto. Once an arc is generated, a fault current continuously flows through the arc. Therefore, there is a problem that the fault current is not reliably interrupted.
In order to solve this problem, Korean Patent No. 1183508 and Japanese Patent Application Publication No. 1984-068128 propose DC circuit breakers that extinguish an arc generated in a mechanical switch using a resonance current. In the conventional DC circuit breakers, in order to interrupt a fault current, an arc generated when the mechanical switch is switched off due to a fault is extinguished using a technology in which the arc is extinguished by making a zero current which is formed by superposing a resonance current (reverse current) on a fault current flowing through the arc in the mechanical switch.
However, the conventional DC circuit breakers have a problem that interruption speed is slow because the resonance current is generated through multiple resonance cycles. In addition, since the conventional circuit breaker consists of a single resonance circuit and a single mechanical switch connected together, it is possible to interrupt only a fault current flowing in one direction with respect to the mechanical switch.
In addition, the conventional DC circuit breakers have a problem that they have a high transient recovery voltage (TRV), which is a voltage applied between two contacts of a circuit breaker after a fault current is interrupted. Specifically, as to a high voltage DC circuit breaker, after a fault current is interrupted, a high TRV is applied between two contacts thereof under a certain circuit condition of a system. In this case, for reliable interruption of a fault current, the DC circuit breaker needs to withstand the TRV so that no current can flow between the contacts thereof. However, since conventional DC circuit breakers have a high TRV, a dielectric breakdown between the contacts is likely to occur in the DC circuit breakers. In order to solve this problem, additional measures, such as injection of gas, are required.